You might want to look at the definition of the fill.
If you can make the basic vectorial fill component to be as large a unit as possible, it might reduce time and even conversion file sizes.
Say for instance you have a horizontal lines fill 85mm apart in the vertical direction. Try to define the x length as 50m, rather than a small units of say 100mm. The y distance will be 85mm. If you have a 10m wide wall, the number of horizontal lines will now be minimal than if you had set the horizontal lengths as 100mm.
Hope I'm clear enough.
Haneef Tayob
Aziz Tayob Architects
AC23 INT rel 3003, OS X 10.14.6 iMac 3.3ghz i5 dual monitor, 24GB RAM